Earthquaker Devices - Ghost Echo  [traced]

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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 15 Apr 2013, 21:35

i had the same thing happen to me. it could use a clean boost after it. i dont know if that is normal for the production units though. glad my transfer worked out for you :D
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Re: Earthquaker Devices Ghost Echo [guts]

Postby nativetrash » 16 Apr 2013, 15:48

Thanks for the transfer! Is there anything that can be changed on the board to give it more volume? I tested it w/ my bass into my ad200 head and it cut the volume more than 50% so I couldn't even really use it
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Re: Earthquaker Devices Ghost Echo [guts]

Postby destro » 16 Apr 2013, 17:07

Production units do not have volume loss. I'd audio probe until you find where the volume loss is at and then you would at least be able to start narrowing down where the problem might be.
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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 17 Apr 2013, 01:11

i compared the schematic from earlier in this topic that i copied and they are identical. i also looked at the datasheets for the TL074 and PT2399 and i dont see any reason why it would be dropping so much volume. the 10K's between pins 1&2 and 8&9 of the 074 are already creating a boost by a factor of 10. i dont know enough about tweeking circuits to figure out where else to boost gain on the existing circuit. i suppose i should build an audio probe....... :?
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 17 Apr 2013, 01:36

Did you try a different opamp chip?
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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 17 Apr 2013, 02:38

no i dont have any other kind of quad chip. can you recommend any that might have a higher gain? thanks
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 17 Apr 2013, 04:06

All opamps should have theoretically infinite gain. The gain of the circuit is set by the feedback network. Try a different 074, maybe yours is broken. Otherwise try reducing one of the feedback resistors.
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 17 Apr 2013, 04:14

I've heard that 2399s can be inconsistent, but you should still be getting unity gain through the path. There also might be a problem with my trace...
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Re: Earthquaker Devices Ghost Echo [guts]

Postby nativetrash » 17 Apr 2013, 14:30

I doubt it's a bad chip since both of us are having volume troubles
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Re: Earthquaker Devices Ghost Echo [guts]

Postby square wave » 17 Apr 2013, 15:12

Motter's trace shows gain is being cut in half at U4a (Gain = R9/R15 = 10k/22k = .45). This is right at the reverb input, so I'm not sure if this would affect the overall gain of the pedal, or just the wet path. Maybe these two resistors were accidentally flipped while drawing the schem? That would be my guess, anyways. :D

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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 17 Apr 2013, 15:43

Image

yeah according to accutronics sample circuit above, it would be the 22k that spans the IC, not the 10k. i will try flipping it today/tonite.
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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 17 Apr 2013, 16:37

in somewhat unrelated news: my buddy borrowed mine and said it wasnt working. i just cracked it open and the volt reg connected to the reverb brick got so hot it melted the jumper and the led wire on either side as well as some of the plastic casing on the socket it lives in. so make sure those wires are not touching the regulator. i guess it gets a little hot. it was the input pin that melted its socket casing. any ideas about that one?
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 17 Apr 2013, 20:59

You can try switching around those two resistors (which should give you more gain into the reverb brick), but I'm positive the 10k is in the feedback loop (between pins 1 and 2) and the 22k goes between pin 3 and the parallel R/C pair. See these photos:

Image
R9 is brown black black red (10,000), R15 is red red black red (22,000)

Image
Trace side connections showing R9 between pins 1 and 2, and R15 between pin 2 and parallel R/C pair
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 17 Apr 2013, 21:05

I think the problem is R21 (the series after that final opamp). This is the resistor between the red cap and the electrolytic at the bottom of the first picture in my previous post. Looks like yellow purple black black (4700) to me. Don't know what I was thinking putting 1M there :slap:

BTW I'm not sure what's wrong with the overheating regulator
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Re: Earthquaker Devices Ghost Echo [guts]

Postby induction » 17 Apr 2013, 22:18

I have a pretty good idea about the regulator overheating, though the problem is probably not the regulator itself. The PT2399 is notorious for this: It locks up, then the regulator gets hot, then the chip tries to reboot itself, locks up again, and the regulator keeps overheating. If this persists too long, the chip is destroyed, so if you notice a problem, pull the power cord out immediately. This doesn't happen with all PT2399's, but with a lot of them - they just can't handle a full 5V, but often a slight voltage reduction will stop it from locking up. I've had good luck with a trick I learned on the other forum: put an Si diode between the regulator and the 5V pin on the chip. Often the diode drop is enough to keep the chip from locking up (assuming it hasn't been overcooked already).

I won't make any promises, but it's worked very well for me with Merlin's Small Time circuit, even with a chip that has locked up in the past.

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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 18 Apr 2013, 02:13

Motter wrote:I think the problem is R21 (the series after that final opamp). This is the resistor between the red cap and the electrolytic at the bottom of the first picture in my previous post. Looks like yellow purple black black (4700) to me. Don't know what I was thinking putting 1M there :slap:

BTW I'm not sure what's wrong with the overheating regulator


i cant exactly agree that is a 4k7 resistor, but i also cant figure out which way is up. what spec of resistor are those tiny blue ones?
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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 18 Apr 2013, 02:16

and if its a 4 band resistor, yel purp blk blk is 470, not 4700. so im further confused. :?:
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Motter » 18 Apr 2013, 14:29

Sounds like I've probably made a few mistakes with resistor values. I'll try to take more photos and correctly interpret the colors this time. Really sorry guys
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Re: Earthquaker Devices Ghost Echo [guts]

Postby kodiakklub » 18 Apr 2013, 15:31

no worries at all motter! im very grateful for the work you have done :)
now for the weirdness: i changed the 1M to 4k7 and left the 10k/22k swapped just to see what it would be like. it is now very close to unity gain, so i would say that 4k7 should be a 470R. however, it only passes a clean signal, whether the effect is engaged or not. the knobs do nothing! i hope its the 10k/22k that need to get swapped back or else i might have fried the brick unsoldering it twice yesterday. oh well. onward ho! :horsey:
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Re: Earthquaker Devices Ghost Echo [guts]

Postby Govmnt_Lacky » 18 Apr 2013, 19:12

kodiakklub wrote:and if its a 4 band resistor, yel purp blk blk is 470, not 4700. so im further confused. :?:


From the picture, it definitely looks like a 5 band/1% resistor. It looks to be Yellow, Purple, Black, Black, Brown. This would be a 470 ohm 1% resistor :applause:
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